Odd non-texture based shading effect

[Macross.]

I've been working on creating some visual effect sliders for a project, and encountered an interesting visual oddity.

 

Some of the effects I'm using cause areas on the body to expand, and while most of them work correctly, when the midriff/stomach area is impacted, I started to see an odd shading effect on the top and sides, looking as though something was casting a shadow on them.

 

Because the effect seemed to be the inverse of what the illumination should be creating, I figured there was some sort of issue related to the normal map, and my testing was using the standard CBBE textures, which has a slightly overhung shading effect baked into the normal map:

 

However when I tried modifying the region to match the lower abdomen rgb values, the issue persisted, even with outlandish modifications.

 

To do some testing, I removed the normal texture channel from the body mesh entirely, and found the same issue.

 

I have now tested this without any textures mapped to the body mesh at all, yet the issue persists:

(Generic nord with sliders applied at extreme values for clarity, all body textures removed):

 

 

At this point I must conclude that the visual effect is not texture related, but I'm not aware of what else would cause this. Does skyrim use some other illumination rendering tech I'm missing?

[Harlemrose1]

I've had issues with this all the time in Skyrim. I've bugtested this for hours and still cannot find the solution. However, the SkepticMesh belly actually solves this issue somehow (but it doesn't actually morph the base texture and rather uses its own). See below

 

SkepticMesh - 
Macross/Morph - 

 

Add me on Discord Harlem#8916 if you see this message. I know this is a pretty dead forum though.